The present invention relates generally to apparatus for automatically generating an alarm or shutting off unwanted flow in cases when a massive leak (e.g. as occurs when a sprinkler head is broken off a pipe) occurs in a sprinkling or spraying system.
Automatic sprinkling systems are commonly employed for the irrigation of agricultural crops and of decorative plantings such as lawns and golf courses. It is desirable to provide such irrigation without wasting water. In many areas, for example, water conservation regulations require that sprinkling be carried out during the evening and nighttime hours when air temperatures are lower and less water is lost to evaporation. A significant amount of spray irrigation thus occurs during time periods when it is inconvenient to monitor the progress of the operation.
A common failure mode of sprinkling systems occurs when a sprinkler nozzle and part of the riser pipe to which it is attached are broken off a feeder pipe. This commonly occurs during times when the sprinkler is not in use and an unseen riser is struck by a vehicle (e.g. a mowing machine) or kicked by a person or animal. Subsequently, when the sprinkling system is next operated, an excessive amount of water gushes from the broken riser while very little flows from other, unbroken, spray nozzles that are served by the same feeder pipe. The excessive amount of water that gushes from the broken pipe may damage plants, erode soil and, in extreme cases, such as when a broken sprayer on a highway median spouts onto a roadway, may cause a safety hazard. Further, if the sprinkler system is located in an area in which water consumption is rationed, the excessive water flow occasioned by the break in the sprinkler system may make the operator liable to penalties for exceeding his maximum allowable water consumption. Moreover, the plantings served by the unbroken sprayheads from which little water flows, will be starved for water and may be thereby harmed if the broken sprayhead is not repaired. Since automatic sprinkling system are commonly operated unattended, a broken sprayhead may not be noticed until damage to some of the plantings becomes visibly obvious.
Spraying systems that are used for purposes other than irrigation are also subject to failures caused when one of a set of spray nozzles is broken. For example, if a spray nozzle is broken from a sprinkler system used to control flammable dust on a coal conveyor, dust reduction may be inadequate and a hazardous condition may ensue.
Prior art leak detection systems measure flow rate to determine when a pipe breaks. To use a system of this sort, one must ensure that the maximum flow rate that will occur during normal sprinkling operation is substantially less than the minimum flow rate that will be found if one sprinkler nozzle is broken. This constraint is generally satisfied in irrigation sprinkler system that provide multiple spray nozzles (e.g. 5 to 10) that are controlled by a single zone valve. However, many sprinkler systems provide a multiplicity of such sprinkler zones with a single master timer that is used to schedule the sequential operation of each of the multiple zones. In multi-zone systems it is desirable, because of the cost of the leak detection and control device, to provide a single master leak detector to monitor and control flow to all of the zones controlled by a single timer. Thus, the use of a prior art leak detection and control system requires that the maximum normal sprinkling flow rate from any zone must be substantially less than the minimum flow rate that can occur if a sprinkler nozzle is broken off. Because the flow rates of sprinkler nozzles and the sizes of pipes used as feeders may vary from zone to zone, this constraint is not always satisfied. Thus, prior art leak detection methods are only applicable on systems that are designed to provide a balanced flow of water to the various zones of the system.
The use of prior art leak detection systems is further complicated by the requirement that the flow rates for normal and broken pipe situations must be determined at the time of installation and the leak detection and shutoff equipment must be calibrated at that time.
Turning away from the immediate application area of sprinkler systems, one finds that there is a substantial body of prior art on detecting leaks in piping systems by recourse to acoustic detectors. This art relies on discriminating between `normal` sounds that are generated by fluid flowing through a pipe of some predetermined diameter and `leak` sounds that are generated when the fluid leaks out through a small hole. Because the hole is much smaller than the pipe, the acoustic frequencies generated by flow through the hole are much higher than those generated by flow through the pipe. Thus, prior art acoustic leak detectors, beginning with the method proposed by T. J. Bell, in U.S. Pat. No. 267,825, use the presence of high frequency acoustic signals as indicative of a leak. Extraneous low frequency signals may be filtered out of the acoustic signals to enhance leak detector performance, as is taught in U.S. Pat. No. 3,413,653. A system that discriminates between various types of leaks, each of which creates a characteristic high frequency sound, is taught in U.S. Pat. No. 3,500,676.
The prior art of using acoustic means to detect large leaks in a piping system includes U.S. Pat. No. 4,736,763, wherein Britton et al teach the use of an economical piezoelectric transducer and a tunable low-pass filter, the averaged output of which is compared with threshold values that correspond to acoustic signals generated by small, low flow leaks that the system tolerates. By this means, they propose to shut down water supply systems in buildings in which a pipe has broken (e.g. an unoccupied vacation home) while tolerating minor leaks such as a dripping faucet.